Tap changing system



Dec. 8, 1931. R HELD 1,835,481

TAP CHANGING SYSTEM Filed Jan. 10, 1929 Position INVENTOR Russell/ 7. F'z'eZd.

' ATTORNEY Patented Dec. 8, 1931 UNITED STATES PATENT OFFICE RUSSELL M. FIELD, OF SHARON, PENNSYLVANIA, ASSIGNOR TO WESTINGHOUSE ELEC- TRIO & MANUFACTURING COMPANY,

A CORPORATION OF PENNSYLVANIA TAP CHANGING SYSTEM Application filed January 10, 1929. Serial No. 331,578.

My invention relates to tap-changing equipment for transformers and has particular application for changing the tap connections to transformer windings of power "if transformers, without removing load from the transformer.

In the operation of power systems and especially where two separate power systems are interconnected, it is frequently necessary '19 or desirable :tovary thetap connections to the transformer windings for the purpose of varying the voltage ratio between the primary :and'secondary windings connected to the separate power systems. It is also frequently desirable to vary the tap connections to :auxiliiazry transformers, that are connected, in "an out-of-phase relation, to the main transformer windings connected to one of the power systems, in order to vary the phase I angle relation between the voltages of the interconnected power systems. It is desirable, in such cases,that the tap-changing operastionsibe made without removing load from. the transformer so as not to interrupt the a service of the power systems.

Power transformers used to transmit large hlocksosf power usually carry relatively high currents, and, :at relatively high voltages.

, The switches for connecting the power circuit conductors tothe transformer taps, must therefore, he built to carry these heavy currents and be insulated for the high voltages of the system. Sw-itchesdesignedfor breaking' heavy currents :at high voltages are expensive' to build, and are subject to greater hazards during-operation, than are switches which operate when load has been removed from the switch, or'which are required to interrupt relatively "low currentsat decreased voltages. h

An object of my invention is to provide a tap-changing system for changing the'connectionslbetween apower line conductor and a transformer winding, adapted for use with a transformer, without removing load therefrom, and wherein the current-interrupting switches :of the system arerequired to operateiat -a'voltage much less than that of the a power system, and to interrupt in most cases a current much less than that of the power system.

A second object of my invention is to provide such a tap-changing system wherein the number of effective voltage steps shall exceed the number of tap connections.

My invention is described with reference to single phase transformer windings, but it will be obvious to those skilled in the art that there may be a plurality of such windings connected together to form a polyphase system, and that my invention has application tozmany systems where it is desired to change tap connections to a transformer windin My invention will be better understood? by reference .to the accompanying drawings in which:

Figure 1 is a diagrammatic view of circuit-s and apparatus illustrating one preferred embodiment of my invention; and

Fig. .2 is a sequence chart showing the sequence of operation of the several switches which maybe actuated by any suitable operating mechanism such, for example, as a cam type controller.

Referring to the drawings, a transformer 11 is illustrated having windings 12 and 13 connected respectively to power circuit conductors 14 and 15, and power circuit conductors 16 and 17. The conductor 17 is connected to the transformer winding 13 through one of the transfer switches, 18 or 19,and one of the tap switches 21, 22, 23 or 24. Transformer windings 29 and 31 are included respectively in circuit with the transfer switches 18 .and 19, and, from the secondary windings of a transformer 32 which is provided with a primary winding 33 energized from a suitable alternating current source, such as the conductors 34, 35. The winding 33 maybe grounded at one end, as illustrated at 36, or in the middle to limit the voltage of this winding above ground potential to a predetermined value, when the winding is open circuited.

The tap-connecting switches 21, 22, 23 and 24 and the transfer switches 18 and 19 are effective to introduce one of the windings 29 or 31 of the transformer '32 in circuit with the conductor 17, and the reversing switches 25 and 26, or27 and 28, are effective to ener- V transformer tap to which it is connected.

The several switches may be operatedeither manually or automatically by any suitable controller in accordance with the sequence operation shown in Fig. 2. I

The' auxiliary transformer 32 is so designed that, when energized, the windings 29 and 31 produce a voltage that is equal to onehalf of the voltage between adjacent tapsof the winding 13, that ,are connected to the switches 21, 22,23 and 24. The reactances of these windings are relatively low so that when the transformer 32 is deenergized and the'power circuit conductor'17is connected to one of the tap-switches 21, 22, 23 or 2 1, the voltage of the eonductor 17 will correspond veryclosely to that of the tap to which it is connected. With a given tap connection to the conductor 17, the auxiliary transform er32 is energized in the one or in the other direction by closing onev pair of reversing switches 25 and 26, or 27' 'andf28. T he volt age of the power circuit conductor 17 will then correspond to the voltage of apoint on the transformer winding 13 that is midway between the transformer'tap' to which it is connected and the next higher or lower trans; former tap of the series, depending upon the direction of energization of the auxiliary transformer 32'. I The numerals reading from left to right across the top of the chart of 2 correspond to controller positions having definite p,

voltage ratio values and the positions indicated by the letters a, b, 0, (Z, c, f, correspond to intermediate, or transitory, switch positions which are effective only during a tapchanging operation, while the controller is passing from one tap position'to another. The numbers, reading from the top to the -bottom, at the left of the diagram, refer to r the correspondingly numbered switches shown in Fig. 1.- The circles in the chart of Fig. 2 indicate that the switches designated by the numbers-at the left of the chart are closed on the controller positions indicated at thertop ofthe chart. I v i [In the controller; position 1 of'Fig. 2, it

' will be noted that switches 18, 21, 25 and 26 are closed, thus connecting the power circuit conductor 17 through the'transfer switch 18, the windin 2a of the auxiliary transformer, and the tap-changing switch 21, to the lowest connection of transformer. winding 13., The switches 25 and 26 are closed, thus producing a voltagein the winding 29 that.

decreases the voltage between the conductors 16' and -17 below thevoltage between the conductor 16 and the switch 21, by'auamount that is equal to halfof the voltage between versing switches 27 and 28 are closed, thus energizing the transformer winding 29 in a directionto increase the voltage between the power -C11C111t conductors 16 and 17 to that value which it would have if the conductor 17 were connected to the winding 13 midway between the tap connections leading from the transformer winding to the tap switches21' and22. r

The next position of the controller, which produces a change in the voltage ratio of the transformer, is indicated by the number 4 at the top of the diagram in Fig.2 and is reached by two intermediate switching'operations indicated by the controller positions a and b. In position fa r, all; of the switches shown closed on controller position 3 remain closed and switches l9 and 22 are also closed. The winding 31 of the auxiliary transformer 32, which isqconnected between the tap'switch 22 and the transformer switch 19, produces a tap voltage equal to one-half the voltage between adjacent transformer taps, and,'in'controller position a, this voltage is subtracted from that of the trans former voltage at the tap connection corresponding to switch 22. Stated in another way, the transformer winding 3l,'when connected between the tap switch22 and the conductor 17 withthe connection shownin the controller position a, subtractsfrom the voltage of the tap switch '22 an amount equal to one-half the voltage between the tap switches 21 and 22, and the transformer winding 29 addsto the .voltage of the tap switch 21 an equal amount. The voltage of the conductor 17, therefore, remains at a value corresponding to a, pointy on the transformer winding 13 midway'between .the, taps connected to the switches- 21 and 22. Inthe controller position b, switches 19, 22, 27

and 28 remain closed and switches 18 and 21 arein their open-circuit position, thus sup plying the same'volta'ge to the powe r circuit conductor '17. In the controller position 4,

quenceof operation of the switches maybe followed'by further reference to the chart shown in Fig. *2.

It will be noted that all of the voltage ratio changing steps of the system are reached by the operation of one pair of reversing switches 25, and 26, or 27 and 28, so that the transfer switches 18 and 19 and the tapconnecting switches 21, 22, 23 and 24, when operated, do not interrupt power flow on any part of the transformer winding.

With two tap-connecting switches, such as the switches 21 and 22, closed, and with the two transfer switches 18 and 19 closed, there is a possibility that a very small circulating current may flow through the loop circuit thus formed, in case the voltages of the windings of this loop circuit are not exactly balanced. The transfer switches 18 or 19 in opening under this condition would interrupt this circulating current, but its value is so small that it has no particular significance. It will be noted that the reversing switches 25, 26, 27 and 28 are connected to a relatively low voltage source of alternating current 34 and 35, representing a relatively small amount of power so that their operation interrupts relatively small quantities of power as compared with that being transmitted by the transformer, and by the power circuits connected thereto.

Many modifications may be made in the arrangement of the apparatus and circuits, from that described in the illustrated embodiment of my invention, and I do not wish to be limited other than by the scope of the appended claims.

I claim as my invention:

1. In a taps-changing system for transformers, a transformer winding and power circuit conductors connected thereto, a plurality of transformer taps and tap connecting switches associated therewith, two transfer switches, an auxiliary transformer having a winding connected in circuit with each of said transfer switches, said auxiliary transformer windings being arranged to be connected in circuit with said power circuit conductor by means of the associated transfer switch and certain of said tap connecting switches.

2. In a tap-changing system for transformers, a transformer winding and power circuit conductors connected thereto, a plurality of transformer taps and tap connecting switches associated therewith, two transfer switches, an auxiliary transformer having a winding connected in circuit with each of said transfer switches, means including said tap connecting switches and said transfer switches connecting said power circuit conductor in sequence to the several taps of said transformer winding, adjacent taps being connected through different windings of the auxiliary transformer, and means for energizing said auxiliary transformer.

33. In a tap-changing system for transformers, a transformer winding and power circuit iconductors connected thereto, a pluralityof transformer taps and tap-connecting-switches associated "therewith, two transfer switches, an auxiliary transformer having a :winding connected in-circuit with each of midtransferswitches,said auxiliary transformer 'windings being arranged to beconneeted in circuit with said power circuit conductor by means of the associated transfer switch and certain of said tap-connecting switches, and means for energizing said auxiliary transformer comprising a source of alternating current and a plurality of pairs of low voltage switches for connecting the auxiliary transformer to the source.

'4. In a tap-changing system for transformers, a power circuit comprising a pair of conductors, a transformer winding connected' to said power circuit and provided with a plurality of tap connections equally spaced along said winding, means comprising a plurality of tap switches and two transfer switches for connecting one of said powercircuit conductors to selected tap connections, an auxiliary transformer having two secondary windings each connected between one of the transfer switches and alternate tap switches, and means for energizing said windings to produce a voltage in each equal to one-half the voltage between adjacent tap connections of said transformer winding.

5. In a tap-changing system for transformers, a power circuit comprising a pair of conductors, a transformer winding connected to said power circuit and provided with a plurality of tap connections equally spaced along said win-ding, means comprising a plurality of tap switches and two transfer switches for connecting one of said power-circuit conductors to selected tap connections, an auxiliary transformer having two secondary windings each connected between one of the transfer switches and alternate tap switches, means for energizing said windings to produce a voltage in each equal to one-half the voltage between adjacent tap connections of said transformer, and means for reversing the direction of energization of said auxiliary transformer windings.

6. In a tap-changing system for transformers, a power circuit comprising a pair of conductors. a transformer winding connected to said power circuit and provided with a plurality of tap connections equally spaced along said winding, means for connecting one of said power-circuit conductors to selected tap connections comprisinga plurality of tap switches, two parallel circuit paths each ineluding a transfer switch and a secondary winding of an auxiliary transformer and connected to different alternate tap switches, and means for energizing said auxiliary transformer windings to produce a voltage in each that is equal to one-half the voltage of said transformer winding between' adjacenttap connections.

7 In amp-changing system for transformers,'a power circuit comprising a pair of conductors, a transformer winding connected to said power circuit and provided with a plurality'of tap ;connections, means for connecting one of said power-circuit conductors-to selected tap connections comprising a plurality oftapswitches, anuauxiliary transformer vcomprising two secondary windings for connection between adjacent tap switches and said power-circuit conductor and each adapted to produce a Voltage equal to one-half the voltage between adjacent tap connections, and

means comprising low-voltage reversing switches for controlling the energlzatlon of said auxiliary transformer.

.In testimony whereof, I have hereunto subscribed myname this 3rd 'day of January,

. RUSSELL M. FIELD. 

